JLPT N3. Used in both writing and conversation.
さえ is a versatile particle that is used most commonly with the affirmative conditional to place emphasis on one thing, e.g. If only I had time, I could travel the world. In this case, さえ takes the place of the object particle.
さえ [VERB: ～ば]
You will often see it used the verb “to exist”: さえあれば.
ちょっとした機会さえあれば成功できると思う。
If I just had half a chance I think I could make it work.
暇さえあればいろいろな計画が実現できるだろう。
If I only had time I could realize some many plans.
お金さえあれば明日のことを心配せず毎日を自由に過ごせるだろう。
If I just had money I could spent every day freely without worrying about tomorrow.
さえ can also take the same role asでも when used without the conditional. The meaning is identical, but さえ has a stronger emphasis.
彼の電話番号って？現在どこに住んでいるかさえわからないよ。
His phone number? I don’t even know whereabouts he’s living now.
足が痛くて歩くことさえ無理です。
My foot hurts—even walking is impossible.
さえ can also be appended to the verb stem, but this structure is rarely used either in conversation or in writing.
[VERB: STEM] さえ すれば
そのポイントに合意してくれさえすれば他は合理的な妥協点を見つけられるかと思います。
If you could just agree to this point, then as for the rest I think we can find a reasonable compromise.